The mechanism of GA1 action: is GA1 synthesis separated from its site of action?

--R. G. Winkler and M. Freeling

An understanding of the spatial and temporal relationship between the synthesis of plant hormones and their action (plant growth regulators) is necessary to understand their roles in plant growth and development. Mosaic analysis was employed to test cell and organ autonomy of the plant growth regulator GA1. Maize d1 is defective in the biosynthesis of the biologically active gibberellin, GA1. Mosaic maize plants were generated that contained sectors of GA-synthesis deficient tissue (d1) in otherwise normal plants. Sectors hemizygous for d1 were identified with the linked carotenoid marker cl1. We examined d1 sectors for variations in cell size and for altered growth. Sector boundaries were examined for distortion of cell shape and size. All smaller sectors (<1 cm wide) indicated that GA1 was diffusible over small distances. However some distortion in cell growth was observed in larger sectors indicting possible undergrowth of GA-deficient tissue.

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